A long time ago, I worked on a project involvingnterpolation of sampled data. It was a "13 pointmoving cubic". Oddly, I remember that term,but nothing else, though I do remember it involveda bunch of coeffciients from a published table.A moving average filter, probably, though perhapsit was a smoother, i.e. not real time.

I have no idea, then or now, the derivation of theformula. Can anybody guess what it was, or thetheory, or point me to a reference?